1. Field of the Invention
The present invention relates to a semiconductor device comprising an electronic circuit and a method for manufacturing the semiconductor device, and more particularly to electrical protection for the electronic circuit.
2. Description of the Background Art
In a semiconductor device according to the prior art, a surge caused by static electricity is sometimes propagated with a high voltage or a great current to an electronic circuit provided therein.
Accordingly, there has been a problem that the electronic circuit provided in the semiconductor device is broken by the surge. In a semiconductor device having a SOI (Silicon On Insulator) structure, particularly, an electronic circuit provided therein is easily broken by the surge. FIG. 33 shows an example of a section of the semiconductor device having the SOI structure. In FIG. 33, the reference numeral 13 denotes a p-type semiconductor region in a SOI substrate (hereinafter referred to as a semiconductor substrate), the reference numeral 111 denotes a SOI layer (semiconductor layer), the reference numeral 14 denotes a buried oxide film, and the reference numeral 112 denotes a MOS transistor provided on the SOI layer 111 and forming an electronic circuit, a gate G, a source S and a drain D being shown. The buried oxide film 14 has a very poor thermal conductivity. For example, SiO.sub.2 has a thermal conductivity of about one hundredth as compared with single crystal Si. Consequently, when the surge is propagated between the source S and the drain D, the temperatures of the source S and the drain D are raised so that the source S and the drain D are easily broken.